FT-891 MOX no output

Can't figure out the MOX feature in my new FT-891. Supposed to give carrier output, i.e. for adjusting an external tuner when working SSB. In the '891, the process appears to be: F key > Function 2 > MOX > press the MULTI knob. When I do that, I get a few more amps on the d.c. power supply and the red transmit light comes on, but zero RF output, in any mode. Only way to tune the antenna is set CW mode, use a straight key, and go key down. No help so far in the Yaesu Op manual, Advance manual, Google, etc. What's the secret?

WB2WIK, right, no output on *any* mode including CW. I'm used to my trusty old FT-767GX, with the MOX button on the front panel. Press it and you get full carrier output, no matter what. Gotta have it to adjust the tuner.